As our earth orbit and spin around the sun, the sun direction in Singapore changes throughout the year. The afternoon sun is generally in the west direction.
More precisely, from March To September, the afternoon sun is in the north-west direction. From September to March, the afternoon sun is in the south-west direction.
So, for east facing unit, you get no afternoon sun throughout the whole year.
For west facing unit, you get afternoon sun throughout the whole year.
For north facing unit, you get afternoon sun from March to September.
For south facing unit, you get afternoon sun from September to March.
You can see the exact sun direction from this sun direction chart for Singapore
http://www.gaisma.com/en/location/singapore.html
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http://singaporenewshub.blogspot.com/2015/01/online-usa-retailers-that-offer-free.html